The Rules of Flat Track Roller Derby

2.4 - Jams

2.4.1 - A period is divided into multiple jams. There is no limit to the number of jams allowed in each period.

2.4.2 - A jam may last up to two minutes. Jams begin at the jam-starting whistle and end on the fourth whistle of the jam-ending signal (see Section 2.9 - Whistles).

2.4.3 - There are 30 seconds between jams.

2.4.4 - If one or more skaters are not completely in bounds at the jam-starting whistle, those skaters will not be permitted to join the jam in progress. No penalty will be issued.

2.4.5 - If skaters are in bounds but not in position at the jam-starting whistle, they will be subject to False Start penalties (see Section 6.13.1 and Section 6.13.22).

2.4.5.1 - Jammers are in position and ready if they are entirely in bounds, and on or behind the Jammer line when the jam-starting whistle is blown.

2.4.5.2 - Blockers are in position and ready if they are entirely in bounds, behind the Pivot line, and in front of the Jammer line when the jam-starting whistle is blown.

2.4.5.3 - Pivots are in position and ready if they are entirely in bounds, on or behind the Pivot line, and in front of the Jammer line when the jam-starting whistle is blown.

2.4.6 - Jammers and Pivots are permitted to put on their helmet covers after the jam has started. However, they must have their helmet cover on their head or in hand before the jam-starting whistle. A helmet cover cannot enter a jam in progress.

2.4.7 - The jam is over when an official calls it off with four short whistle blasts. The jam ends on the fourth whistle, whether or not the whistles were inadvertent or incorrect.